For what it's worth, tukaani is how you spell toucan (the bird) in Finnish, and Lasse is a common Finnish name; the site being previously hosted in Finland is very plausible.
Yeah according to their website[0] it looks like majority of the past contributors were Finnish so nothing odd about the hosting provider. On the same page it says that Jia Tan became co-maintainer of xz in 2022.
0: https://tukaani.org/about.html